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<title>2.3.1 Truth Value Testing
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<H2><A NAME=
"SECTION004310000000000000000"></A><A NAME=
"truth"></A>
2.3.1 Truth Value Testing
Any object can be tested for truth value, for use in an
<tt class=
"keyword">if
</tt> or
<tt class=
"keyword">while
</tt> condition or as operand of the Boolean operations below.
The following values are considered false:
<a id='l2h-
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></a><a id='l2h-
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></a><a id='l2h-
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></a><a id='l2h-
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></a><a id='l2h-
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></a>
<a id='l2h-
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></a>
<a id='l2h-
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></a>
<LI>zero of any numeric type, for example,
<code>0</code>,
<code>0L</code>,
<code>0.0</code>,
<code>0j
</code>.
<LI>any empty sequence, for example,
<code>''
</code>,
<code>()
</code>,
<code>[]
</code>.
<LI>any empty mapping, for example,
<code>{}
</code>.
<LI>instances of user-defined classes, if the class defines a
<tt class=
"method">__nonzero__()
</tt> or
<tt class=
"method">__len__()
</tt> method, when that
method returns the integer zero or
<tt class=
"class">bool
</tt> value
<code>False
</code>.
<A NAME=
"tex2html6"
HREF=
"#foot3425"><SUP>2.5</SUP></A>
All other values are considered true -- so objects of many types are
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Operations and built-in functions that have a Boolean result always
return
<code>0</code> or
<code>False
</code> for false and
<code>1</code> or
<code>True
</code>
for true, unless otherwise stated. (Important exception: the Boolean
operations
"<tt class="samp
">or</tt>"<a id='l2h-
99' xml:id='l2h-
99'
></a> and
"<tt class="samp
">and</tt>"<a id='l2h-
100' xml:id='l2h-
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></a> always
return one of their operands.)
<a id='l2h-
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></a>
<BR><HR><H4>Footnotes
</H4>
<DT><A NAME=
"foot3425">...False.
</A><A
href=
"truth.html#tex2html6"><SUP>2.5</SUP></A></DT>
information on these special methods may be found in the
title=
"Python Reference Manual"
>Python Reference Manual
</a></em>.
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<span class=
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2005.
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